In the microelectronics industry, sheets of semiconductor materials are typically sawed into individual wafers using dicing saws. With dicing saws, there are several possible concerns including thermally and/or mechanically-induced cracking and or adhesion loss between adjacent layers, poor mechanical strength, moisture absorption and/or time-dependent behavior due to the use of coolant, texture effects and poor thermal conductivity. Of these possible concerns, thermally and/or mechanically induced cracking and/or adhesion loss and moisture absorption are significant. Large tensile and shear stresses are imparted at the cut zone, which can lead to cracking and/or adhesion loss leading to delamination between adjacent layers. Further, the use of coolant during sawing can lead to moisture absorption and time-dependant behavior.
One approach to reduce potential problems with mechanically induced delamination is to reduce saw speed. However, this reduces throughput and productivity. In addition, the potential problems relating to moisture absorption still remain.
Another approach is to cut or scribe a trench wider than the saw in the areas to be sawed using a laser device generating a single beam. The beam scribes through low dielectric constant (low-k) and metal layers, for example, and stops at the silicon. Following the laser scribing, the saw is used to cut through the silicon and singulate the wafers. The area removed by the laser acts as a crack stop and ensures that these cracks do not propagate into the wafer and potentially affect the electrical performance of a finished integrated circuit contained on the wafer. The disadvantage of using a single laser beam is the requirement of cutting a fairly wide trench in the low-k and metal layers.
Still another approach is to scribe using a laser device generating at least two beams to make two trenches, one on each side of the area to be sawed. This eliminates the potential problem of cutting a wide trench. The operation of such a system is generally shown in FIG. 6. FIG. 6 illustrates a planar workpiece 200. A pair or laser beams impact workpiece 200 at impact points 202 and 204. Impact points 202 and 204 are orthogonal to an X-axis 206 of the workpiece 200. A pair of parallel trenches may be scribed on the workpiece 200 by either moving the workpiece 200 or the laser beams along X-axis 206.
However, using two or more beams to cut parallel trenches requires additional processing time to reorient the workpiece 200 and/or the impact points 202, 204 if it is desired to scribe parallel trenches along a Y-axis 208. Such reorientation increases processing time.